Monarch butterflies need milkweeds like trout need water. Without milkweeds or water both species do not survive. Fish aside, this article looks at different species of milkweeds found throughout the United States and also at creatures besides monarch butterflies that are tied to these plants.
But before we go there, let’s take a closer look at milkweed members of the Asclepias genus.
Modern-day taxonomists have moved the Asclepias members into the Dogbane family, Apocynaceae from the formerly recognized Milkweed Family, Asclepidaceae. The Dogbane family includes a wide diversity of tropical to temperate plants which includes trees to annuals. Many species in the family have the milky-white sap that our milkweed herbs are known for and which is toxic to many creatures with a few exceptions.
Monarch caterpillars being one of the most noted exceptions to this toxicity, as the caterpillars consume the sap and foliage, they accumulate cardiac glycosides within their bodies which make them inedible. This doesn’t mean that one or two won’t be eaten by a jay or other bird; but it does mean they’ll be the last ones consumed by that bird as it regurgitates its unpalatable prey.
The monarch butterfly caterpillars, along with other members of the “Royal” butterflies, the Queens and Viceroys, need these host plants for this life stage. This critical stage is the reason that milkweeds have gotten their due in local media – plantings of milkweeds, once considered noxious weeds, are sprouting up all over the country in city parks, community gardens, backyards, and conservation areas as they are important host plants for these butterflies.
Interestingly, though the sap of the milkweed is toxic, many Native American tribes consumed the stems, leaves or pods either raw or after parboiling the plants to reduce the toxicity levels.
Milkweeds Across the United States
One species, Showy milkweed (A. speciosa) is widely distributed from the Midwest to the West Coast. Often growing in moist, waste areas such along irrigation ditches, in fallow pastures or agricultural fields, this species has big clusters of pinkish flowers which fade to yellow, and large, stout leaves perfect for protecting a fragile monarch egg. This milkweed is also the one a western gardener will find in nurseries or available by seed, unless of course you collect seed yourself. Some individuals have had good success with digging up and dividing roots, then replanting in soil to get plants started.
Another widely distributed milkweed that gardeners can grow is Butterfly weed (A. tuberosa). With yellow to orangish flowers and narrower leaves, this colorful milkweed grows from New England to Florida and west to the Rocky Mountain states. Native Americans chewed the tough roots to treat pleurisy and lung ailments, hence, another common name is Pleurisy root. Though a host plant for monarch larvae, this plant also attracts numerous adult butterflies in search of nectar. These butterflies transfer sacs of pollen between plants as they walk over and around the crown-shaped flowers.
In the Mohave Desert, two of the many milkweed species that grow here are Desert milkweed (A. erosa) and Mexican whorled milkweed (A. fascicularis). Both have lance-shaped leaves, although the whorled milkweed’s leaves are very narrow. Both bear clusters of greenish-white flowers and produce pods that split open lengthwise to reveal seeds with fine silky hairs which act as parachutes enabling the seed to travel away from the parental plant. Native Paiutes in the Mohave Desert utilized the long, tough fibers of the Mexican whorled milkweed to plait together creating string or rope which was woven into strands for cloth or used to make nets to capture rabbits.
Two common species that are widely distributed from the Midwest to the east are Swamp milkweed (A. incarnata), also known as Pink milkweed, and Common milkweed (A. syricaca). Both are excellent monarch host plants and also attract other pollinators.
In the Southwestern United States, a low-growing milkweed known as Antelope-horns milkweed (A. asperula), also known as Spider milkweed, grows in sandy soils and is covered with tiny hairs. The seedpods are curved resembling the horns of an antelope, hence the common name.
In the East, look for White milkweed (A. variegata) and Purple milkweed (A. purpurascens) along with other milkweed species. A cool gardener-geeky note is that scientists can determine where a population of monarchs hatched by analyzing the chemical isotopes of the sap found in the plant with those inside the butterfly.
Other Milkweed Insects
Because the nectar and pollen of milkweeds doesn’t contain toxic glycosides, there are a host of other insects which visit these flowers or feed on the foliage. Butterflies include fritillaries, checkerspots, monarchs, viceroys, and queens, and then there are several true bugs and a few moth caterpillars which are also tied to the plants.
Tussock moths and Milkweed tiger moths are two moth species which lay their eggs on milkweed plants. The caterpillars don’t feed exclusively on the toxic compounds just like the monarch’s caterpillars, rather they feed on the leaf tissues and avoid or limited the amount of milky sap they ingest. The caterpillars chew through a leaf vein which allows the toxic sap to drip out of the leaf. Their bright red or orange warning colorations indicate avoidance due to their toxicity.
Two milkweed bugs, named the Large milkweed bug and the Small milkweed bug, may also be present on milkweed plants later in the season. Their bright red or orange colors with black patterning is also meant to warn predators away, just like the tussock moth’s coloration. These two true bugs feed on the sap and developing seeds. Females lay eggs within the seedpods where the young larvae feed on the seeds.
Answering the Call to Conservation
With over 100 species of milkweed growing in North America, there are many options for gardeners to include local species in their gardens. Using native species adapted to the climate and growing conditions raises the survival rates of these milkweeds. Not only are you creating habitat for hosting monarch butterfly caterpillars, but also providing food resources for other butterflies and insects. Seed sourcing locally also conserves the local gene pool, a factor that is often overlooked but one of importance, too.
A handout from the Monarch Joint Venture, a partner organization helping preserve monarchs and their migrations, is a good source of information, planting tips, and references for protecting these special creatures and their host plants.